Method of defoliating cotton plants



United States Patent 3,401,030 METHOD OF DEFOLIATING COTTON PLANTS Robert V. Berthold, South Charleston, W. Va., and Richard A. Herrett, Raleigh, N.C., assignors to gnion Carbide Corporation, a corporation of New ork 1 No Drawing. Filed Sept. 9, 1964, Ser. No. 395,298 3 Claims. (Cl. 71-69) ABSTRACT OF THE DISCLOSURE Cotton plants are defoliated by applying to them imidazopyridines especially 3H 6 chloromidazo[4,5-b] pyridine.

This invention relates to methods and compositions for the defoliation of plants. More particularly, this invention is concerned with methods and compositions for defoliating cotton plants, and with the use of highly specific cotton defoliant imidazopyridines.

In harvesting agricultural crops with mechanical equipment, the plant leaves often interfere with effective operation of the harvesting machine. In addition, the quality of the harvested product may be deleteriously affected by the presence of leaves. For example, in the case of cotton, the presence of leaves results in a discolored harvested crop. With the increase in mechanized harvesting of crops, it has become increasingly important to find efficient methods for defoliation.

It has long been known to treat crop plants chemically with the object of inducing defoliation and thereby facilitating harvesting of the crop by mechanical means. However, most of the chemicals used heretofore, particularly inorganic chemicals such as the chlorate-borate mixtures, achieve this object primarily by subjecting the plant to what may be termed biological shock, characterized by freezing of the leaves and chlorosis, stunting, burning of the plant, and the like, as opposed to pure defoliation in which the abscission cells in the leaf petiole are selectively affected to cause the leaves to fall off while leaving the remainder of the plant unharmed. To achieve substantially pure defoliation is particularly important when treating cotton plants where the presence of burned leaves frozen to the plant can deleteriously affect both yield and quality of the harvested crop.

The imidazopyridines contemplated for use in this invention possess the ability, to a degree not approached by prior materials, to induce highly selective pure defoliation of cotton plants. In addition, use of these imidazoi pyridines has been effective in defoliating actively growing cotton normally only treated with great difficulty and, furthermore, has been found to substantially obviate regrowth problems encountered when employing known defoliants. Furthermore, the imidazopyridines disclosed herein have the ability to suppress regrowth of cotton foliage once defoliation has taken place. All these desiderata are achieved when employing extremely low (relative to the quantities of known defoliants normally required) concentrations of these materials.

Accordingly, an object of this invention is to provide highly specific cotton defoliants. Another object is to provide imidazopyridines which possess highly specific cotton defoliant properties. A further object is to provide methods and compositions for defoliating cotton plants using as the active defoliating agent one or more imidazopyridines disclosed hereinafter. A specific object is to provide methods and compositions for defoliating cotton plants using 3H-6-chloroimidazo[4,5-b]pyridine as the active defoliating agent. These and other objects will become apparent to those skilled in the art to which this invention pertains from the ensuing description thereof.

( km m Rl The imidazopyridines used in this invention can be represented by Formulae I, II, III, and IV:

(I) II (II) III N (IONA-q 1R1 wherein R is either halogen, especially chlorine, bromine or iodine, and particularly a middle-halogen (chlorine or bromine), amino, nitro, or lower alkyl, with the proviso that each R is on a different ring carbon atom; R is hydrogen or lower alkyl; 11 is an integer of from 0 to 3, inclusive; and the acid addition and quaternary ammonium salts thereof. When R and R are lower alkyl, the lower alkyl group preferably contains from 1-8 carbon atoms, with from 1-5 carbon atoms most preferred. The lower alkyl group can be branched or straight chain and is preferably unsubstituted, but can bear simple substituents which do not adversely affect the desired properties of the imidazopyridines disclosed herein. This invention intends to include mixtures of compounds represented by the aforementioned formulae.

The imidazopyridines of this invention can be characterized as imidazo[b]pyridines and imidazo[c]pyridines as represented by 1H-5,6,7-substitutedl imidazo[4,5-b] pyridines (Formula I), 3H-5,6,7-substituted imidazo- [4,5-b]pyridines (Formula III), 1H 4,6,7 substituted imidazo[4,5-c]pyridines (Formula II), and 3H-4,6,7-substituted imidazo[4,5-c]pyridines (Formula IV), respectively. Of the aforementioned imidazopyridines, those preferred are the imidazo[b]pyridines, particularly the 1H-5,6, and/or 7-halo substituted imidazo[4,5-b]pyridines and 3H-5,6, and/or 7-halo-substituted imidazo- [4,5-b]pyridines, especially those wherein halo is chloro or bromo. The compounds of this invention also can be characterized as substituted azabenzimidazoles.

Preferred imidazo[b]pyridines can be specifically rep resented by Formulae V and VI:

wherein each R is either methyl, chloro, bromo, nitro, or amino; and n is an integer of from 0 to 3, inclusive, preferably 1.

Representative imidazopyridines encompassed Within this invention includes, for example,

1H-6-chloroimidazo [4,5 ,-b]pyridine, 3H-6-chloroimidazo [4,5 -b] pyridine, lH-6-chloroimidazo [4,5 -'c] pyridine, 3H-6-chloroimidazo [4,5-c] pyridine, lH-7-chloroimidazo [4,5-b] pyridine, lH-S-chloroimidazo [4,5-b] pyridine, 3H-7-chloroimidazo [4,5-b] pyridine,

3H-5 -chloroimidazo [4,5 -b pyridine, 3I-I-6-brornoimidazo [4,5-b] pyridine, 3H-6iodoimidazo [4,5-b] pyridine, 3H-5,6,7trichloroimidazo[4,5-b1pyridine, 3H-5,6-dichlorcimidazo[4,5-b] pyridine, 3H-5,6,7-tribromoimidazo [4,5-b]pyridine, lH-S,6,7-trichloroimidazo [4,5-b] pyridine, lH-tribromoimidazo [4,5-b] pyridine, 3H-5,6-diiodoimidazo[4,5-b] pyridine,

3 3H-5,6,7-triiodoimidazo [4,5- b pyridine, 3H-5 chloro-6-bromoimid azo [4,5 -b] pyridine, 3I-I-S-chloro-6-iodo-7-bromoimidazo [4,5-b pyridine, 3H-6-methylimidazo [4,5-b pyridine, 3H-6-ethylimidazo 4,5-b pyridine, 3H-6-propyli rnidazo [4,5b] pyridine, 3H-6-isopropyli inidazo [4,5 -b] pyridine, 3H-6-tert-butylimidazo [4, 5b] pyridine, 1H-5 ,6,7,-trimethylim'idazo [4, 5-b] pyridine.

in boiling Water and filtered while hot through activated charcoal. The cooled filtrate deposited 3H 6 chloroimidaZo[4,5-b]pyridine as a pale yellow-solid. The yield of 3H-6-chloroirnidazo[4,5-b] pyridine was 77 percent. A second recrystallization from water produced almost colorless white needles of 3H 6 chloroimidazo[4,5+b] pyridine, M.P. 237238 C.

Arzalysis.Calculated for C H N Cl: C, 46.92; H, 2.63; N, 27.36; Cl, 23.09. Found for C I-I N Cl: C, 46.74;

3H-6-chl'oro-7-methylimidazo[4,5-b]pyridine, 10 H, 2.40; N, 27.08; Cl, 23.09. 3H-6-nitroimidazo[4,5-b]pyridine, The following examples will illustrate the cotton de- 3H-5,6-dinitroimidazo[4,5-b1pyridine, foliant properties of the imidazopyridines of this inven- 3H-5 ,6,7-trinitroimid azo [4,5 -b] pyridine, tion. 1H-6-aminoiniidaz0[4,5-'b] pyridine, EXAMPLE II 3H-6-aminoimidazo[4,5-b] pyridine, p 3H-5,6,7-triaminoiimidazo[4,5-b] pyridine, In a series of greenhouse tests, 3H 6 chloroimidazo 3H-6 chloroimidazo[4,5-b]-2 methylpyridine, [4,5-b]pyridine was formulated by dissolving one gram 3I-I-6-chloroimidazo[4,5-b]-2-isopropylpyridine, of 3H-6-chloroimidazo[4,5-b] pyridine in 50 milliliters of 3H-4-ohloroimidazo[4,5-c]pyridine, acetone in which had been dissolved 0.1 gram (10 percent 3H-4-bromoimidazo[4,5-c]pyridine, of the weight of the pyridine) of an alkylphenoxypoly- 3H-4-nitroimidazo[4,5-c]pyridine, ethoxyethanol surfactant, as an emulsifying or dispersing 3H-4-aminoimidazo[4,5-c]pyridine, agent. The resulting solution was mixed into 200 milliand others, liters of water to give 250 milliliters of a suspension containing the pyridine in finely divided form. The thus-pre- The imidazopyridines used herein possess the advantage, in addition to their unusually high degree of activity, i i ir fg z z 'g g g Z Z g i in agricultural applications in that they are Organic commillion parts of solutioi which was subsequ ritly dilu ed fsggg gi t g g gggiiiza5311253? resldues m the S011 to give test solutions of 1250 p.p.'m., 625 p.p.m. and 312 The imidazopyridine which has performed best in the of the pyndme as notedlm Table practice of this invention is the 3H-halo-substituted TWO Sets of Young cotton fi 'g imidazo[b]pyridine, 3H-6-cliloroimidazo[4,5-b]pyridine. 2 5 9;; li ggg i fi il i i g 211$; This latter compound has been shown to exhibit outstandand second Set with d gfi y gleaves fully ex in ro ertie as a s ecific defoliant for cotton lants. It i als o h ai a m arked c pacity to suppress regrowtii of cot- Panded and the fifth and Slxth leaves l appearmg (10 ton foliage once defoliation has taken place. The marked weeks old.) were Placed a p y igi cotton defoliant properties of 3H-6-chloroimidazo[4,5b] sprayed Wlth h test Solutions contammg t e y or pyridine was not expected in view of pyridine compounds 30 Seconds using a hand Sprayer Set at 40 Youpg known to possess herbicidal activity and to kill cotton .control plains were sprayed wlth f check sohmgm contamplants mg no active compound and with the proprietary ma- 40 terials S,S,S-tributylphosphorotrithioate and sodium cis-3- s s z 2:3 gg jggg 5x5355 5 igi chloroacrylat-e formulated in a manner similar to the 3H- action of the appropriate 2,3-diaminopyridine with from 6h1omlm1dazo[45"b]pyndme formulauon' plants about 98 to about 100 percent by weight formic acid. The were removed to the greenhousehaind hfald 5 imidazopyridine product can be isolated by removal of at letstfourteen days after t p i U 6 degree 0 defoliation and the severity of any in ury were observed excess formic acid by stripping at reduced pressure. The 1b 1 e to d r ted as follows imidazopyridines are obtained via this route in high yield, f j 1 f 1 an a and in most cases are sufliciently pure to be used as resi- F22 foliation due products; however, purification may be effected by fiefolfation recrystallization from suitable solvents known'in the art. d rat d foliation The following example will illustrate the imidazopyri- :313 defeoligtion dines of this invention and their preparation. 1:110 defoliation EXAMPLE I Injury or desiccation rating:

5=plant dead 3H-6-chloroimidazo[4,5-b]Pyridine 4zsevere desiccation 28 grams (0.195 mole) of 5-chloro-2,3-diaminopyri- 3=moderate desiccation dine was added to ml. of 98 percent by weight formic 2=slig ht burn 1 acid. This mixture was then heated under reflux for one 1=no in ury hour. Excess formic acid present was removed under re- Table I sets forth the results obtained from the aforemenduced pressure. The resultant solid residue was dissolved 6O tioned procedure using the aforementioned ratings.

TABLE I Concentration of active compound in parts per million Age (weeks) of cotton 1,250 625 312 Def Des 2 Def. Des Del Des.

4 3H-6-chloroimidazo 5 4 3 4 3 [4,5-b]pyridine. 5 5 4 2 4 Sodium ClS-3-0hl0l0- 4 4 3 3 2 3 i0 4 4 4 4 i 2 4 S,S,S-tributyl phosphoro- 3 3 3 2 3 2 trithioate. 10 do 4 2 4 3 2 3 Deioliation 1 and Desiccatiou rated as horeiiiabovc defined with reference to Table I.

It can be seen from Table I, that the cotton plants treated with 3H-6-chlorimidazo[4,5 b] pyridine showed only moderate to slight effects of leaf desiccation or other herbicidal effects with good defoliation.

EXAMPLE III 3H-6-chlorimidazo[4,5b]pyridine, the most preferred imidazo[b]pyridine disclosed herein, was also tested as follows: vigorously growing cotton plants, having about 7 to 8 fully expanded leaves, were sprayed with aqueous solutions of 3H-6-chloroirnidazo[4,5-b]pyridine and the known defoliant sodium cis-3-chloroacrylate to give the dosages indicated in Table II, infra, in pounds of active compound per acre. The Water volume used was equivalent to 59 gallons per acre for all dosages. Fourteen days after spraying, the plants were examined and each test compound Was rated on the basis of percent defoliation taken as an average of three tests. The results are set forth in Table II.

TABLE II Pounds of active Defoliation compound in percent per acre SH-G-chloroimidazo [4,5-b1pyridine 96. 2 Do M 96. 6

It can be seen from Table II that at all concentrations tested, 3H-6-chloroimi-dazo [4,5-b] pyridine was superior to sodium cis-3-chloroacrylate in cotton defoliation.

Table III sets forth the percent of defoliation as an average of three tests wherein the ratings were made seven teen days after treatment.

When preparing the 'defoliants used in this invention the compounds described above can be admixed with an inert carrier. This carrier may be a liquid or a solid and should contain surface active agents. Suitable surface active agents are alkylphenylpolyethylene glycol ethers, dimeric alkylated aryl polyether alcohols, and the like. A stickerspreader such as glycerine or a nonvolatile solid polyethylene glycol, may also be added to insure adhesion of the formulation to the plant after spraying.

Water is an ideal liquid carrier but suitable organic solvents may be employed. Formulation in Water suspensions presents the simplest and easiest method of application. Alternatively, application may be made in the form of dusts or powders where the active compounds are admixed with a solid carrier such as clay, attapulgite,

pyrophyllite, or talc. The concentration of the active ingredient in the final formulation, liquid or solid, may be from about 0.1 to about 10 percent by Weight, with from about 0.1 to about 1.0 by weight preferred.

Generally, the effective amounts of the imidazopyridines range from about 0.1 to about 10 pounds per acre with from about 0.25 to about 2 pounds per acre preferred. The precise concentration, within the broad range, to be used in any given field will depend on the specific soil conditions, the variety and age of the cotton plants to be treated, the amount of foliage present and environmental factors such as temperature, light, humidity and rainfall. For example, as the cotton plant approaches maturity, it is more readily defoliated, thus requiring less chemical. Actively growing highly vegetative cotton plants are generally more diiiicult to defoliate. However, it is one of the features of the compounds contemplated for the use in this invention that actively growing cotton plants may be defoliated.

What is claimed is:

1. Method of selectively defoliating cotton plants which comprises applying to the plants a defoliatingly eiiective amount of an imidazopyridine of the formulae selected from the group consisting of:

wherein R is halogen with the proviso that each R is on a different ring carbon atom; R is hydrogen; n is an integer of from 0 to 3, inclusive.

2. Method of selectively defoliating cotton plants which comprises applying to the plants a defoliatingly effective amount of 3H-6-chloroirnidazo[4,5-b] pyridine.

3. Composition for selectively defoliating cotton plants containing a defoliatingly elfective amount of 3H-6-chloroimidazo [4,5-b]pyridine and a major amount of an inert carrier therefor.

References Cited UNITED STATES PATENTS 2,693,408 11/1954 DAmico 712.5 2,844,577 7/1958 Acker 71-2.5 3,069,253 12/1962 Sousa 71--2.5

FOREIGN PATENTS 938,052 9/ 1963 Great Britain.

LEWIS GOTTS, Primary Examiner.

G. HOLLRAH, Assistant Examiner. 

